So what’s the secret to the net-zero energy (NZE) performance of the Packard Foundation headquarters in Los Altos, Calif., designed by EHDD? It’s not some humongous photovoltaic array that simply stands in for conventional energy sources. Sure, there is a 285-kilowatt photovoltaic system, but that is modest for a 50,000-square-foot office building. The real key was to put the two-story building on an energy diet, minimizing electricity consumption while treating natural daylight as a precious commodity. Enhanced envelope design, a highly efficient HVAC system, compact offices, and a reduced plug load also played their parts.

The daylighting strategy focused around achieving ambient “perceptual brightness” from windows and skylights, so that occupants would not feel tempted to flip the light switch on during regular hours. The LEED Platinum-certified building is split into a pair of 40-foot-wide wings with a courtyard in the middle. The upper floors have linear skylights, while the lower floors have tall ceilings that allow light from the windows to percolate deep inside.

The building’s energy performance, which yielded a net positive result in its first year of operation, depends on continual adjustments to the envelope, both by occupants and by computer systems linked to sensors. For example, electric lighting automatically dims when daylight is strong enough. Interior window shades are user-controlled by day, but at night they automatically reset to the raised position so that the building soaks in the morning sun.

Of course, keeping the sun’s unwanted heat out is just as important as letting its light in. When sunlight is too intense, automated exterior shades cover the windows on the southwestern elevation. All windows are triple-glazed and the envelope is detailed to eliminate thermal bridging, measures which also prevent the loss of heat in cooler weather. When outdoor air temperature is near optimal, a notice appears on staff members’ laptops inviting them to open a window.

All of these responsive adjustments and details reduce the demand for mechanical conditioning. The building gets by with a thrifty little HVAC system that relies only on solar-powered electricity for heating, and, for cooling, radiant beams and panels that circulate water chilled in the night air and stored underground.

It also doesn’t hurt that the climate of Los Altos, a once-agricultural town in Silicon Valley, is mild, if not balmy. The forgiving climate also allows the central courtyard to function as an everyday workspace and meeting space—an outdoor room that consumes no energy and brings daylight to the interior. Along the street, curbside rain gardens and the locally sourced, natural building materials give public expression to the foundation’s ecological intentions.

On top of everything else, a special factor in this project was the client’s deep interest not only in occupying a sustainable building, but also in rethinking transportation, travel, and even food consumption choices to reduce the carbon footprint of the organization as a whole. Instead of building an $8 million, carbon-intensive underground garage to provide the code-mandated 160 parking spots, the client received special permission from the city to provide only 67 parking spots along with free employee rail passes and a shuttle from the train station.

Click here to see all of the 2014 AIA COTE Top Ten Green Projects. Scroll down for more images, along with performance data and project team and materials information. Stay tuned for profiles of this year's winning firms on Ecobuildingpulse.com, along with additional coverage of this year's Top Ten in the Spring issue of ECOBUILDING Review.

Credit: Jeremy Bittermann

Credit: Jeremy Bittermann

Credit: Jeremy Bittermann

Credit: Jeremy Bittermann

BY THE NUMBERS
Project completion date: July 2012
Building gross floor area: 49, 161 square feet
Estimated percent of occupants using public transit, cycling, or walking: 18
Daylighting at levels that allow lights to be off during daylight hours: 81
Lighting power density (watts per square foot): 0.60
Percent of views to the outdoors: 90
Percent of spaces within 15 feet of an operable window: 80
Percent reduction of regulated potable water: 69
Potable water used for irrigation: Yes
Percent of rainwater from maximum anticipated 24-hour, two-year storm event that can be managed on site: 90
Total EUI (kBtu per square foot per year): 22
Net EUI (kBtu per square foot per year): -4
Percent reduction from national median EUI for building type: 76
Third-party rating: LEED Platinum, International Living Future Institute Living Building Challenge
Total project cost as time of completion (land excluded): $37.2 million